The present invention relates to brake assemblies, and more particularly, to such brake assemblies of the type intended for use with fluid pressure actuated devices such as hydrostatic motors. Although the present invention is not actually limited to being used with a fluid pressure actuated device, the invention does rely in part on the presence of pressurized fluid for its operation, and therefor, the invention will be described in connection with a hydrostatic motor.
Although the present invention may be included advantageously with many different types of fluid pressure actuated devices, it is especially adapted for use with a low-speed, high-torque gerotor motor, and will be described in connection therewith. As is well known to those skilled in the art, brake assemblies are an important feature of many low-speed, high-torque gerotor motors, especially when such motors are utilized for vehicle propel applications. Many vehicles propelled by hydrostatic drive circuits, including gerotor motors, are operated on hilly terrain and on work sites involving grades, such that some sort of motor braking capability is essential.
For years, many of the gerotor motors made and sold commercially, both by the assignee of the present invention as well as by others, have had the motor valving disposed "forwardly" of the gerotor gear set (i.e., toward the output shaft end of the motor), thus having nothing disposed "rearwardly" of the gerotor gear set except for an endcap. The present invention is not so limited, but is especially adapted for use with gerotor motors of this type, and will be illustrated and described in connection therewith.
In many vehicle applications for low-speed, high-torque gerotor motors, the motor can have either a parking brake or parking lock, the term "lock" being preferred in some instances because it is intended that the parking lock be engaged only after the vehicle is stopped. In other words, such parking lock devices are not intended to be dynamic brakes, which would be engaged while the vehicle is moving, to bring the vehicle to a stop. However, the term "brake" will generally be used hereinafter to mean and include both brakes and locks, the term "brake" being somewhat preferred to cover a device which can be applied gradually and to distinguish from a device which would operate either fully engaged or fully disengaged.
For many years, those skilled in the art have attempted to incorporate brake and lock devices into gerotor motors, as opposed to merely adding a brake package on the motor output shaft. The desire for a brake assembly to be incorporated into the motor is based on the need to keep the overall motor package as small and compact as possible, whereby a motor brake can be added, but without the need to re-design the surrounding portion of the vehicle. Examples of such brake devices are illustrated and described in U.S. Pat. Nos. 3,616,882 and 4,981,423. In the device of U.S. Pat. No. 3,616,882, a braking element is disposed adjacent the forward end of the gerotor star, and is biased by fluid pressure into frictional engagement therewith. Such an arrangement involves a certain degree of unpredictability of performance, in view of variations in clearances, etc. Such an arrangement also requires a substantial redesign of the wear plate and forward bearing housing of the motor. In the device of U.S. Pat. No. 4,981,423, there is a multi-disc brake assembly which is of the "spring-applied, pressure-released" type. The arrangement of U.S. Pat. No. 4,981,423 also requires almost total redesign of the forward bearing housing, and also results in a much larger bearing housing. In addition, the disc pack is in splined engagement with the output shaft and, therefore, must be able to brake or hold the full output torque of the motor, thus necessitating that the discs, the spring, and the apply/release piston all be relatively larger.
On many of the vehicles of the type which would use gerotor motors equipped with spring applied, pressure released type brakes, there are frequently situations where it is necessary to be able to tow the vehicle. Unfortunately, while the vehicle is being towed, and the vehicle hydraulic system is not operating, the motor brake is spring applied, such that the vehicle could not be towed. It is now known to provide a separate source of hydraulic pressure, such as a hand pump, which can be used to pressure release the brake in those situations where it is necessary to tow the vehicle. However, the addition of a separate pump simply for the purpose of manually releasing the brake adds substantially to the overall complexity and cost of the motor and brake system.: In addition, when the vehicle is to be operated normally again, there must be a mechanism for relieving the hydraulic pressure holding the brakes in their-released position, adding even further to the cost and complexity of the system.